Turbine compressor plant



Dec. 28, 1948. F. NETTEL EI'AL 2,457,594

I TURBINE COMPRESSOR PLANT Filed May 14, 1942 3 Sheets-Sheet 1 Fig.5 u

IN V EN TORS BY M 7mm.

1948- F. NETTEL ETAL TURBINE COMPRESSOR PLANT 3 Sheets-Sheet 2 Filed May14, 1942 HOTWIND 136 TORS . HOTWIND INV quantity and/or pressure.

Patented Dec. 28, 1948 OFFICE TURBINE COMPRESSOR PLANT Frederick Nettel,Manhasset, and Johann Kreitner, New York, N. Y.

Application May 14, 1942, Serial No. 443,000

9 Claims. 1

This invention relates to a novel method of producing compressed gas,preferably air, particularly for consumer systems of widely fluctuatingflow resistance, causing large fluctuations of requirements in gasquantity and/or pressure.

Known plants for gas compression provide power producing means indriving relation to air compressing means, and conduit means connectingthe outlet of said air compressing means to the consumer system. Anychange in said consumer system thus necessarily reacts directly on thecompressing means, so that the entire performance of these plantsdepends on the performance characteristics of said compressing means.

Certain types of compressors and blowers permit only comparatively smalldecreases in gas quantity at their outlet, while any substantialreduction causes a dangerous unstable condition generally known assurging. This phenomenon has so far excluded the otherwise veryefflcient multistage axial flow compressor from many uses, and evenradial type compressors often require inconvenient and complicatedregulating systems to operate blow-off valves discharging certainquantities of gas when the quantity consumed falls under a certainminimum, which varies with the resistance offered by the consumersystem.

It is the basic object of this invention to provide a. gas compressingsystem wherein the compressor means remain practically unaffected by anychanges occurring in the consumer system, so that the highly efllcientmultistage axial flow compressors with their known very narrow surginglimits may be used to supply consumer systems of the most difficultrequirements as regards This invention permits to use such normallyextremely surge-sensitive" compressors even where at certain times therequired gas quantity drops to zero, which is equivalent to operation ofa plant as known in the art against closed pressure valve, without anydanger of surging and without the use of any blow-ofi valve. Thus newwide fields of application are made accessible to the axial flowcompressor of superior efliciency, from which it has been barred so far.

This object is achieved basically by compressing the gas to a pressuresubstantially higher than that of the consumer system, and by expandingit in turbine means interposed in the gas stream between the compressormeans and the consumer system, so that no direct conduit connectionexists between the compressor means and the point in the gas streamswhere variations in presexpansion stages.

2 sure and quantity may occur. The turbine means by their inherentcharacteristic of periormance, act as a very effective buffer, shieldingthe compressor means from the effects of variations in the consumersystem.

Where the turbine means are located close tow the compressor means, theymay preferably be arranged in driving relation with the latter. Wherehot compressed gas may be supplied, the gas stream may preferably beenergized by heating it in front of the turbine means.

The blower system as described may be in driving relation withadditional power supply means, or may be self-sufllcientin power. Forthe latter purpose it is preferable to compress more gas than isrequired in the consumer system to a pressure substantially higher thanrequired, energize it by heating, expand it in multistage turbine means,and branch oil the quantity required for the consumer system at asuitable intermediate stage of the turbine means, while the remainder isexpanded to the starting pressure. Such an arrangement offers a stillmore effective shielding of the compressor means from changes inoperating conditions, due to the high pressure stages of the turbinemeans interposed as buffer between compressor and consumer system. Thereason for this shielding effect is found in the well-known performancecharacteristic of extraction-backpressure steam turbines, andconsequently of any elastic fluid turbine, in which changes in theextraction quantity and/or pressure are compensated inside such turbineswithout tangible reaction on the supply source of the working fluid,which in the case of steam turbines is the steam boiler, and in case ofgas turbines, the compressors. The conditions are similar to those inextraction steam turbines working under constant admission pressure,which are known to consume a practically constant quantity regardless ofvariations that may occur in the lower Thus also in the system accordingto this invention, the working conditions of the compressor supplying agas turbine remain almost unchanged, even if the supply pipe to theconsumer system, i. e. the extraction pipe, is completely closed. Thegas which cannot flow to the consumer, due either to smaller demand, orwith the supply pipe closed altogether, will simply flow through the lowpressure stages of the gas turbine which acts, so to speak, as anautomatic useful blow-off.

If the turbine means interposed between compressor and consumer systemare, .for example, of an expansion ratio of two or more, a ten per cent3 change of pressure in the consumer system causes less than two percent change of pressure at the compressor outlet. This shielding eifectincreases rapidly with increasing expansion ratio of the interposedturbine means; with an expansion ratio of about four it amounts to apractically complete isolation of the compressor means fro wateveroccurs in the consumer system.

Where the compressor need only be protected against moderate variationsof pressure or resistance in the consumer system, a device of utmostsimplicity may be provided by interposing only one or two stages ofturbine means without heating of the gas in front of them. In such casesthe turbine blading is simply added to the compressor blading as anadditional stage or stages within the same casing and on the same rotor,thus forming an integral compressor of improved surging characteristics;The power requirements of such compressor, as compared with one ofstraight compression to the consumer pressure, i. e. without turbinestages, is of course increased due to the internal losses caused by theadditional compression and re-expansion, but these losses are very smallin case of only one or two interposed turbine stages.

The great advantages of inserting turbine means between compressor meansand consumer system become particularly apparent if means are providedfor keeping the rotative speed of the compressor means and interposedturbine means constant, such as speed governors influencing the heatingof'the compressed gas, or complementary coupling to an A. 0. motor orgenerator connected to an electric power system of substantiallyconstant frequency. The practically constant pressure at the compressoroutlet, achieved by the interposing of turbine means, together with aconstant speed imposed by the abovementioned design measures, results ina constant delivery characteristic of the system. In other words, thecompressor can be designed to operate always near its best efliciencypoint, which is advantageous both for economy and convenience ofoperation. Besides, the new system makes the highly efhcient axial flowcompressor with its very steep speed-quantity characteristic availablefor satisfying constant-quantity requirements involving large pressurevariations, while running at constant speed driven for exampleelectrically.

Certain embodiments of this invention are well suited for thesimultaneous production of power, other than that required for drivingthe compressors, still others offer additional advantages in efliciencyand/or performance by reheating the whole or part of the gas or airduring expansion. Examples of such embodiments will be described as thisspecification proceeds.

The invention will be now described more specifically in its, preferredapplication to the production of wind for metallurgical furnaces andsimilar consumers. 1

It is known to produce wind by means of combustion turbine-drivencompressors. The known arrangements compress air to the pressurerequired in the furnace, and lead one portion ofthe air to the furnaceas wind, while the rest is generally compressed further and passedthrough the cycle of the combustion turbine driving the compressor.

' Such known arrangements are not widely used because they offer littleadvantage over other known drives. In addition some of them pollute 31cwind by the products of internal combusefficient manner. It is aspecific object to economically produce -wind of low moisture content,and unpolluted by It is also known in the art of air drying, to cool theair either before or after compression. Cooling after compression ismore effective because the partial pressure of the water vapor at a,certain temperature represents a smaller fraction of the total pressureof the compressed air, so that the water weight represents a smallerfraction of the air weight.

.Modern blast furnace operation requires a sharp drying of the wind tothree grains water per 0. ft. at atmospheric pressure, or less. Therequired dryness was often unobtainable by cooling with naturallyavailable cooling media under the required wind pressure, which in mostcases is too low for this purpose. For example, 30 to 35 lbs. per sq.in. absolute are necessary in blast furnaces. Cooling is further limitedby the temperature of the available cooling medium, mostly water of60 todeg. F. Thus it became neces sary to intensify drying by using chilledwater or even brine, produced in rather complicated and expensiverefrigeration apparatus.

It is another object of this invention to improve the thermal emciencyof wind production in industrial furnaces and in particular in blastfurnaces, and of the blast furnace plant as a whole.

It is still another object to combine production of compressed air withpower production in an products of combustion.

It is finally an additional object of this invention to reduce the sizeand weight of the necessary apparatus for the production of a givenquantity of compressed air.

The economy of wind drying is achieved by cooling the wind at apressu'rehigher than the 'furnace pressure, which is made possible by the processdescribed above. A modification provides for cooling between stages ofcompression, and/or after compression; it is only essential for thisinvention that the last cooling is carried out at a pressuresubstantially higher than the required wind pressure.

This invention thus makes double use for the intercoolers provided,namely for intercooling of the working fluid in a combustion turbinecycle and for drying the furnace air to a p t mined degree, 1

A further improvement of the method described above is obtained by usingthe excess air expanded to near-atmospheric pressure as combustion airfor heating the whole of the compressed air before it enters said firstpower producing expans'lon means, an d/or for wind heating.

Still higher efllciency is realized by a process comprising cooledcompression of more air than n is required in the furnace, heating itafter compresslon in a surface type heater, expanding it in powerproducing expansion means to'the required furnace pressure, leading theexcess air at furnace pressure to said surface type heater,

burning fuel in it to heat the high pressure air sideration of theensuing description of the em-,

bodiments of'apparatus for carrying the invention into effect which areillustrated in the accom-- panying drawings by way of non-limiting examZ ples in which:

Fig. 1 shows a plant for gas compression in which the compressor iscoupled to a synchronous motor, and the turbine to a synchronousgenerator.

Fig. 2 represents an embodiment with both compressor and turbine coupledto a synchronous motor.

Fig. 3 shows another embodiment of arrangement as per Fig. 2 withcompressor and turbine arranged in a common casing.

Fig. 4 is a combination of'arrangement as p r Fig. 2 with heating of thecompressed gas before partial re-expansion. A synchronous machine iscoupled to compressor and turbine.

Fig. 5 is a combination of arrangement as per Fig. 4 in which theturbine is of the extractionbaclrpressure type.

Fig. 6 represents a plant with an intercooler for wind drying, surfaceheater, and an air turbine from which the wind is discharged from anintermediate stage to the furnace.

Fig. 7 shows an embodiment with two inter- 4 coolers and one wind heatertowhich the combustion air is supplied from the turbine exhaust.

Fig. .8 is another combination with a reheater for the excess air, anduse of the turbine exhaust first for wind heating and thereafter forheatin the air at top pressure.

Fig. 9 is still another combination with tw coolersfor wind drying, asurface air heater for top pressure, an air turbine for expansion of thewind to furnace pressure, a wind heater, a reheater and a second turbinefor the excess air. The turbine exhaust is used in heaters.

Fig. 10 shows another alternative arrangement with an air turbine forexpanding to furnace pressure, an internal combustion-turbine forexpanding the excess air to atmosphere, wlth'separate combustion chamberfor the latter; wind heater and surface air heater are supercharged onthe gas side at furnace pressure.

Fig. 11 shows a simple arrangement without excess air, with onedryer-intercooler,'s'urface air heater and drive by a synchronous A. C.motor designed to run as asynchronous motor during starting.

Fig. 12 represents a high-efllciency' plant for production of hot windwith dryer-intercooler-of the water contact (spray) type, reheating at apressure higher than the furnace pressure, and additional combustionchamber for reheater.

The arrangement as per Fig. l, which represents the simplest embodimentof the new method of gas compression, operates as follows: Gas taken inat i is compressed in multistage axial fiow compressor 2, in drivingrelation with an electric motor 3, to a pressure higher than required inthe consumer system. The latter is represented by pipe 8 with severalbranch pipes .8. The thus compressed gas flows through pipe I4 to gasturbine 5 arranged in driving relation with an electric generator 6. Inturbine 5 the'Sasexpands to the pressure required in said consumersystem, into which it is discharged through pipe I. The power developedby said expansion is utilized in the electric generator 6 which may beconnected to the same electric supply as motor 3 or to another electric,system. The speedsat which compressor and .turbine operate may be thesame or different.

As explained before this arrangement is able to supply gas against agreatly varying pressure or resistance in the consumer system withoutrequiring variation of the rotative speed of the compressor and withoutdanger of surging.

are coupled mechanically with motor 6 supplying the required power. Ifthis set is running at constant speed. driven for example by asynchronous motor, the plant will supply a substantially constant gasquantity into system 8, irrespective of pressure variations in pipe 1within wide pressure ranges.

Where these pressure variations are moderate, an arrangement of extremesimplicity can be provided, such as shown in Fig. 3 where the compressorstages c and turbine stages t are arranged on a common rotor r driven bypower supply means (motor) :2. Thus the gas taken in at i is compressedand re-expanded in the same stator housing s equipped with turbine guidevanes ii, in addition to compressor guide vanes 01. The gas isdischarged at d at a pressure which may vary much more than would bepermissible for an ordinary axial flow compressor.

Where the expansion ratio of the interposed turbine is considerable,heating of the gas in front of said turbine is preferable for eflicientpower production from said re-expansion. Fig. 4 shows such anarrangement. Itoperates as follows:

Air taken in at I is compressed in compressor 2 to a pressure higherthan that required in consumer system 8, thereafter lead via pipe 4 intoa heater coil 4', in which the gas is heated by flame 4". The thusheated gas continues to the gas turbine 15 wherein it expands to thepressure required in the consumer system 8 and is discharged into thelatter through pipe I. Depending on the pressure in system 8 and on theintensity of heating in coil 4', turbine 5 may develop less power thanis consumed by compressor 2. To cover the power deficit, an electricmotor 6, preferably of the synchronous type, is mechanically coupled tocompressor and turbine, maintaining the speed of the whole set constant.Under other working conditions turbine 5 may just cover the requirementsof compressor 2. In this case motor 6 will run at no-load and may beomitted altogether. Under again other conditions turbine 5 may producemore power than required by compressor 2, causing the motor 6 to operateas generator supplying power into the electric system to which it isconnected.

If machine 6 is of the synchronous type, for example, it will under allworking conditions maintain the speed of the set constant, resulting ina substantially constant delivery characteristic, as explained for Fig.2. Taking into consideration the peculiar performance characteristic ofthe axial flow compressor, preferably employed in the examplesdescribed, there are practical limits to the pressure rise in pipe I,but by proper selection of the expansion ratio for turbine 5 thepermissible range of pressures in the consumer system can be made wideenough to permit successful use of the axial flow compressor;furthermore very diflicult supply problem can by this invention besolved by compressor means of constant rotative speed; thus the simpleand cheap condition would require a blow-off valve in the I arrangementsas per Figs. 1-4. The arrangement shown in Fig. 5 is capable o supplyingany gas quantity down to zero without blow-off. Its operation isbasically the same as for Fig. 4, except that more gas, preferably air,

than required in the consumer system is taken in, compressed and heated.Turbine 5' is, more over, in this example an extraction-back pressureturbine with the gas entering through pipe 4. The gas expands to thepressure prevailing in the consumer system 8, into which the requiredquantity is branched off from'an extraction point be: tween stages ofsaid turbine through pipe 1, while the excess gas quantity I expands inthe lower stages of turbine 5' to the starting pressure, be-

ing discharged through pipe 1'. With. motor 6 driving the set atconstant speed, basically the same performance characteristic results asfor Fig. 4. If, however, the requirements of the consumer system 8 dropvery much, or if the pipe 1 is closed altogether by valve 8', part orall the gas not flowing to the consumer system continues to expand inthe lower pressure turbine stages,

as already mentioned. With the turbine 5' properly designed, thecompressor 2 will be little affected by anything that happens in pipe 1,and surging will not occur even with valve 8 closed tight.

The example as per Fig. 6 for production of warm furnace wind operatesas follows: Air ent-ers the first stage compressor H at H, flows throughthe surface intercooler l2, with cooliiiag; Through cooling underpressure part of the mois-. ture contained in the air condenses out andis; discharged at l4. Dried air continues through. conduit I5 into thesecond stage compressor i6, being discharged at top pressure throughpipe l1, to flow-into surface type air heater l8, through. it, asindicated by-dotted line, then through pipe water inlet and outletindicated under H into a second surface heater l9, through the latter asalso indicated by dotted line, and through pipe to the air turbine2 Theaction of the surface heaters will be described later. At the outlet ofstage compressor H the air pressure is high enough to dry it by coolingit with water Y of natural temperature for the requirements of i Inturbine 2| the heated air is expanded to furnace pressure'and thequantity required by the furnace discharged from an appropriate stagethrough pipe 22 to the furnace. The

the furnace.

remainder of the air is further expanded in the lower stages of said airturbine to near-atmospheric pressure, leaving through pipe 23 intochamber 24, disposed between the surface heaters i8 and |9, thencethrough the tubes of heater f8, and to the atmosphere at 25. The heatfor the plant is produced by combustion of fuel, preferably blastfurnace gas, in combustion chamher 26, the fuel entering-through pipe21, and

air from the atmosphere at 28. The hot combustion gases fiowv fromchamber 26 upwards through the tubes of surface heaters I3 and i8 andalso to the atmosphere at 25, heating through heat transfer thecompressed air of said heaters on its way to turbine 2|. In order tokeep the speed of the set practically constant, the fuel valve 29 isinfluenced by speed governor 30 as shown in the drawing. Starting oi theset is effected by electric motor 30' in the usual way.

The alternative as per Fig. 7 for production of hot wind for ametallurgical furnace operates as follows: Air is taken in at 3| throughstage compressor 3|, intercooler 32 with cooling water conections 33,pipe 35, second stage compressor 36 in the same way as in Fig. 6. Drainof moisture through pipe 34. From compressor 36 the air flows at toppressure into after-cooler 31 with cooling water connections 38, outthrough pipe 40, provided with another moisture drain pipe 39, to entersurface heater 4|, passing through it as. indicated bydotted line,thereafter through pipe 42 to the air turbine 43. In the latter the hotair expands to furnace pressure, the quantity required in said furnacebeing discharged at a suitable stage from said turbine through pipe 44,passing thereafter through surface heater 45 as indicated by dottedline, and leaving through pipe 46 as hot wind for the furnace. The'excess quantity of air expands further in turbine 43 to near-atmosphericpressure, beingled thereafter through pipe 41 to combustion chamber 48for the heaters 4| and 45. In chamber 48, fuel entering through pipe 4.)is burned in the air coming from turbine 43 and the 'gases from thiscombustion flow upwards in succession through the tubes of heaters 45and 4|, and to the atmosphere at 50. Thus the combustion heat is used toheat' first the wind in heater 45, thereafter the whole air at toppressure in heater 4|. The after-cooler 31 is provided for such plantswhere the available cooling water is sometimes rather warm(summer-time), so that the cooling after the first stage compressorwould not dry the air to the desired degree. By cooling at still higherpressure the desired drying effect may be achieved even with verywarmcooling water.

. In order to control the temperature in the combustion chamber 48,secondary air may be blown in through a pipe 5| by means of a forceddraft fan 52. Starting of the plant is effected by starting motor 53.

Another alternative arrangement as per Fig. 8 for hot wind productionoperates as follows: The flow of the air, in at 6|, through stagecompressor 6|, intercooler 62 with cooling connections 63, pipe 65,second stage compressor 56, is basically the same as in Fig. 6. Drain ofmoisture through pipe 64. From 66 the air continues through pipe 61 intosurface heater 68, as indicated by the dotted line, then through pipe 69to air turbine 10, expanding therein to the furnace pressure, andleaving through pipe 1|. From that pipe the required wind quantity isbranched off through pipe 1|, to flow through gases from pipe 18 whichstill contain sufficient free oxygen. The thus reheatedgases'flowupwards through the tubes of heater 12 and thereafter -of heater 68, tobe finally discharged to the atmosphere at 8|. Thus the heat of saidsecond combustion is used to heat first the wind, and thereafter thewhole air from the second stage compressor, before said air enters theair turbine 10. Also in this case additional air may be blownintocombustion chamber 19 byfan 82, to control the temperature inchamber 19.

The different combination of a plant for wind production as per drawingFig. 9 operates as follows: The now of the air in at 9|, through stagecompressor 9|, intercooler 92 with cooling water connections 93, drain94, pipe 95, second stage compresor 96, after-cooler 91 with coolingwater connections 98, drain pipe 99 and pipe I is substantially thesame'as shown in Fig. 7. From pipe I00 the compressed air passes throughsurface heater IOI, flowing as indicated by the dotted line, out throughpipe I02 and after brancing off a part of the air through pipe I03, thepurpose of which will become clear later, the wind quantity is expandedin air turbine I04 to furnace pressure. Thereafter the wind flowsthrough pipe I05, then through surface type wind heater I08 via pipe I01to the furnace. The excess air, over what is required in the furnace, isbranched off through said pipe I03 into an internal combustion chamberI04 in which fuel, entering through pipe I05 under pressure, is burned,The products from this combustion flow through pipe I06 to gas turbineI01, expanding therein to near-atmospheric pressure,

and via pipe I08 into combustion chamber I09,

disposed below the surface heaters I06 and IN. These two heaters areconnected on the gas side through intermediate chamber IIO. In chamberI09 additional fuel is burned, entering through pipe III, in the gasesfrom turbine I01 which still contain free oxygen; The products from thiscombustion flow upwards through the tubes of said surface heaters, firstthrough wind heater I06, then through air heater fill and out to theatmosphere at II2. Excess power over what may be required for windproduction may be utilized for example in electric generator II3 coupledwith the turbines. Since it is known in the art to arrange turbines andcompressors in a system on separate shafts, it is an obvious furtheralternative to arrange for example turbine I01 driving generator II3 ona separate shaft. Generator II3 may be so designedas to be used as motorfor starting of the plant.

. The alternative embodiment of the invention as per Fig. 10 operates asfollows: Air is taken in at I2I', compressed in stage compressor I2I',passed through intercooler I22 with cooling water connections I23, pipeI25, through second stage compressor I26 and is at top pressure in pipeI21. Drain of moisture from intercooler takes place through pipe I24.From pipe I21 the air continues through the tubes of regenerative heatexchanger I28, leaving it through pipe I29, to enter thereafter surfacetype heater I30, flowing through it as indicated by the dotted line, andon through pipe I'3I into the air turbine I32. In the latter the airexpands to furnace pressure, being discharged through pipe I33. Fromthis the required wind quantity is branched off through pipe I34 intothe wind heater I35, through which it flows as indicated by dotted lineand finally discharged as hot wind to the furnace through pipe I36. Theexcess air is led through pipe I31 to combustion chamber I38 disposedbelow the surface heaters I35 and I30. Blast furnace gas is compressedin gas compressor I38 to substantially furnace. pressure and fed throughpipe I40 also to combustion chamber I38, wherein it is burned in the airentering through pipe I31 under furnace pressure. The products from thiscombustion flow upwards through the tubes of surface heaters I35, thenI'30, leaving via pipe I to enter gas turbine I42, where they expand tonearatmospheric pressure, passing thereafter via pipe I43 intoregenerative heat exchanger I23. Through the latter they flow asindicated by the dotted line, to be finally rejected to the atmosphereat I44. For metallurgical reasons it is necessary to limit thetemperature in combustion chamber I38. This is done by leading into thatcombustion chamber through pipe I45 with valve I45, a regulatablequantity of compressed air tapped from stage compressor I2I at a pointwhere the pressure is substantially the same as prevails in chamber I38,namely the furnace pressure.

Since the same pressure exists in the wind heater I31 inside and outsidethe heater tubes, these are relieved completely of any stress frompressure, which is particularly desirable due to the very hightemperatures prevailing in said heater.

Fig. 11 represents a particularly simple alternative arrangement whichmay be adopted where the air pressure required by the consuming deviceis comparatively low, or when it may be feasible in the future to allowhigher air temperatures at the turbine inlet. The plant operates asfollows: Air is taken in at I'5I', compressed in stage compressor I5I,flowing thereafter through intercooler I52 with cooling waterconnections I53. Moisture is drained through pipe I54. The air continuesthrough pipe I55 to second stage compressor I56 and thence at toppressure via pipe I51 to the surface heater I58, through which it flowsas indicated by the dotted line. From heater I58 it is led via pipe I59into air turbine I60, in which it expands to the pressure required inthe consuming device, being discharged to the latter through pipe I6I aswarm wind. It is evident that by energizing the compressed air throughheating, the energy produced in the air turbine can be made to cover thecompression work. Heating of the compressed air takes place ina furnacechamber I'62 disposed below heater I58. Air for combustion is taken fromthe ambient atmosphere through valved pipe I63, fuel through valved pipeI54.

.If the resistance in pipe I6I increases, the pressure in that pipe willrise. The air turbine I60 will under this condition develop less powerdue to increasing back pressure and the power deficit must be made up byintensifying the combustion in chamber I62, so as to raise the airtemperature at the inlet to the air turbine I68. The set may also becoupled with a synchronous motor for supplying power, I65,-which may beused also'for starting of the plant.

Certain kinds of furnaces, for example such serving blast furnaces orBessemer converters, require wind of varying pressure with the windquantity constant or varying. If, for example, the same wind quantity isrequired at fifty per cent higher gauge pressure, it is obvious thatmore power has to be furnished into the blower drive. Fig. 12 shows ablast furnace blower plant also suited to fulfill these peculiarrequirements,

ll combined with wind drying and a wind recuperator replacing theconventional stoves (Cowpers) The plant operates as follows: Air istaken in at IBI'to the stage compressor IBI, leaves it at say 3.5 atabsolute through pipe I82, to enter water spray-type intercooler I83,where .it iscooled by water supplied from pump I84 via pipe I84, inlet.valve I85 and outlet valve I85. In such cooler the moisture of the aircondenses into the cooling water.- air of 3.6 at absolute is cooled bywater of deg. C. to +25 deg. C. the air leaving the intercooler throughpipe I82 will have a water contentofabout 0.0056 weight units per weightunit of air (about 3 grains per cbft.) only, which 15 is very desirablefor blast furnace operation. The air is then further compressed to say10 at absolute in stage compressor I86, flows through pipe I81 into-thefirst surface air heater I88,

through the latter as indicated by the dotted line, leaving 'it via pipeI89 to enter the second surface air heater I90, through the latter as asindicated by the dotted line, and thereafter through pipe I9I to airturbine I92 wherein it expands to, for example, 5 at absolute. The'airor partly in parallel on the same shaft or on continues via pipe I93 tosurface type reheater I94, through which it flows as indicated by thedotted line, then through pipe I95 into a second air turbine I95. Whileexpanding in that air turbine, the wind quantity is branched on at theproper pressure, say 2.38 at absolute, while the remainder of the airexpands in the lower stages of turbine I96 to near-atmospheric pressure,leaving through pipe I98. The wind is ledinto wind heater I99, throughwhich it flows as indicated by the dotted line, leavinghot through pipe200 to the furnace. The said remainder of the air from pipe I99 is ledinto combustion chamber 20I, disposed below the wind heater I99. Fuel,for example blast furnace gas, from pipe 202 is led via regulating valve202' into chamber 20I' and burned in air from pipe I99.

As can be seen from the drawing, surface heaters I99, I90, I94 and I88are connected through intermediate chambers 203, 204 and 205, so thatthe combustion gases from chamber 20I flow through said surface heatersin the sequence stated and are rejected finally to atmosphere at 206,

with burner and fuel feed pipe 201 with regulating valve 201'. Provisionis further made for supplying additional air to combustion chambers,

when wind of normal pressure, say 2.38 at absolute, is delivered withlittle or no combustion in chamber 204. If the required pressurerises,'due; to some irregularity in the furnace or for some otherreason, and the wind quantity is not per-. mitted to drop appreciably,the combustion in chamber 204 is intensified by admitting more fuel andair to it through valves 201' and 209, with'the result that the air atentrance to-turbine I 96 is reheated to a higher temperature. Thisreheating increases the power produced in turbine I96, thus allowing tocover the increase in compression work caused by the higher pressure.Starting of the plant is effected by a starting motor of any kind asknown in the art. (Not shown.)

If for example compressed l0 Intermediate chamber 200 is also equipped50 Compared with known plants of gas turbine driven compressors, theplantsaccording-to this invention also furnish a much greater portion ofthe air taken in by the compressor as useful air, which results for agiven useful air quantity (wind quantity) in much smaller and cheaperturbines and compressors. The higher top pressure of the compressed airalso improves the heat transfer conditions in the heaters with aconsequent reduction in size also of these. Finally it deserves mentionthat the outputof the plants according to this invention is lessaffected by seasonal changes in intake air temperatures than is the casein known plants.

separate shafts and what number of intercoolers or reheaters areemployed.

It is understood, however, that the turbine means interposed betweencompressor means and consumer system are preferably of the fulladmission axial flow type.

It is also immaterial what kind of fuel is burned in the surfaceandinternal combustion type heaters, or whether different fuels are used indifierent heaters of the same system. See our co-pending applicationSer. No. 401,703 filed July 10, 1941, now Patent No. 2,394,253.

For the production of wind for blast furnaces it is, however, understoodthat blast furnace gas is the preferred fuel for at least part of theheat produced in the system according to this invention.

We claim:

1. In the method of producing wind for metallurgical furnaces or similarconsumers in air turbine driven blowers, the steps of compressing moreair than required for the furnace to a pressure substantially higherthan the required wind pressure, drying it by cooling it at said higherpressure, compressing it thereafter to a still higher pressure,energizing it by heating it at said highest pressure, expanding it inpowerproducing expansion means to the required wind pressure, branchingoff the required wind quantity into wind heating means, and expandingthe remainder in power producing expansion means to atmosphericpressure.

2. In apparatus for producing wind for metallurgicai furnaces or similarconsumers, the com bination of multistage air compressor means of theaxial flow type, air cooling means interposed between stages of saidcompressor means where the pressure is substantially higher than there-. quired wind pressure, surface type air heating means, fulladmission axial fiow multistage air turbine means for expanding thecompressed 3. In the method of producing wind for metallurgical furnacesand similar consumers in air turbine driven blowers, the steps ofcompressing more air than required for the furnace to a pressuresubstantially higher than the required wind pressure, energizing it byheating it at said higher pressure, expanding it in power producingexpansion means to substantially the required wind pressure, branchingofi the required quantity of wind to the furnace, expanding theremainder in power producing expansion means-to near-atmosphericpressure, burning fuel in said expanded air, transferring heat of saidcombustion through heating surfaces to said compressed air forenergizing it at highest pressure, thereafter rejecting the resultinggases to the atmosphere, and using the power produced in said expansionmeans for supplying the power for compressing said air.

4. In the method of producing wind according to claim 3, the steps ofcompressing air with intermediate cooling between stages of compression,reheating between said first and second expansion means, bothintercooling and reheating taking place at pressures not lower than therequired wind pressure.

5. In the method of producing wind for metallurgical furnaces andsimilar consumers in air turbine driven blowers, the steps ofcompressing more air than required for the furnace to a pressuresubstantially higher than the required wind pressure, energizing it byheating 'it through heating surfaces, expanding it in power producingexpansion means to substantially the required wind pressure, branchingoff the required quantity of wind, thereafter discharging itto thefurnace, reheating the remainder of the compressed air by internalcombustion of fuel in said air, expanding it in power producingexpansion means to near-atmospheric pressure, burning additional fuel insaid expanded air-gas mixture, transferring heat of said last combustionthrough said heating surfaces to said air at its highest pressure,thereafter rejecting the resulting gases to the atmosphere, and usingthe power produced in said expansion means for compressing said air.

6. In apparatus for producing wind for metallurgical furnaces andsimilar consumers, the combination of multistage air compressor means ofthe axial flow type, designed to furnish air of a pressure substantiallyhigher than that required in the metallurgical furnace, air intercoolingmeans interposed between stages of said compressor means, surface typeair heater means, multistage air turbine means, a fuel burning furnace,first conduit means for taking air from the ambient atmosphere into" thefirst stage of said compressor means, second conduit means forconnecting the outlet of said stage compressor to said intercoolingmeans and thence to the second stage compressor means, third conduitmeans for connecting the outlet of said latter compressor means to saidsurface type air .heater means and thence to the inlet of said airturbine means, fourth conduit means for branching off the required windquantity from such intermediate stage of said air turbine means wherethe pressure is substantially equal to the pressure required in themetallurgical furnace and thence to said furnace, fifth conduit meansfor the remainder of the air after its expansion in said turbine meansto near-atmospheric pressure for leading it into said fuel burningfurnace to serve therein as combustion air, sixth conduit means forpassing the combustion gases from said latter furnace, after heattransfer to the compressed air in said air heater means, to theatmosphere, and coupling means between said air compressor means andsaid air turbine means.

7. In apparatus for producing hot wind for metallurgical furnaces andsimilar consumers,

the combination of multistage air compressor means of the axial flowtype designed to furnish air of a pressure substantially higher thanthat required in the metallurgical furnace, air intercooling meansinterposed between stages of said compressor means, surface type airheater means, multistage high pressure and low pressure air turbinemeans, fuel burning internal combustion air heater means, a fuel burningfurnace, surface type wind heater means, first conduit means for takingair from the ambient atmosphere into the first stage of said compressormeans, second conduit means for connecting the outlet of said stagecompressor to said intercooling means and thence to the second stagecompressor means, third conduit means connecting the outlet of saidlatter compressor means to said surface type air heater means and thenceto the inlet of said high pressure air turbine means, fourth conduitmeans for branching off the required wind quantity from the last stageof said high pressure air turbine means where the pressure issubstantially equal to the pressure required in the metallurgicalfurnace, for leading it into said surface type wind heater means andthence to the metallurgical furnace, fifth conduit means for theremainder of the air for connecting the outlet of said high pressureturbine means with the inlet of the said fuel burning internalcombustion-chamber and thence to the inlet of said low pressure turbinemeans, sixth conduit means for said remainder of the air, after ithas'expanded in said low pressure turbine means to near-atmosphericpressure, for leading it into said fuel burning furnace to serve thereinas combustion air, seventh conduit means for passing the combustiongases from said latter furnace, after heat transfer to the wind in saidsurface type wind heater means and to the compressed air at top pressurein said surface type air heater means, to the atmosphere, and couplingmeans between said air compressor means and said air turbine means.

8. The method of preventing surging in flowtype compressors producingcompressed gas for use in consumer systems which are operationallyindependent of the producer system and have widely fluctuating flowresistance comprising the steps of compressing more gas than required insaid consumer systems to a pressure substantially greater than thepressure required, heating said compressed gas, expanding it in powerproducing multi-stage gas expansion means, interposing a part of saidexpansion means in the gas fiow between said compressor and consumersystem by branching off the consumer gas at a point between stages ofsaid expansion means where the partly expanded gas has reached therequired pressure, expanding the remaining gas further, and, using thepower produced in said expansion means for driving said compressormeans.

9. In the method according to claim 8, the step of compressing the gasto an absolute pressure more than double the absolute pressure requiredin the consumer system.

FREDERICK NE'I'IEL. JOHANN KREITNER.

(References on following page) REFERENCES CITED The following referencesare of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Ludewig Feb, 11, 1908 MichellMar, 3, 1914 Mfiller Sept. 12,1916 Lysholm May 22, 1934 Noack Apr. 9,1935 Lysholm Oct. 19, 1937 Harris Nov. 9, 1937 Graemiger May 23, 1939Noack June 27, 1939 Number 2,186,877 2,223,572 2,242,767

16 Name Date Noack "Jan. 9, 1940 Noack Dec. 3, 1940 Traupel May 20, 1941Meyer July 1, 1941 Noack May 12, 1942 Jendrassik Dec. 22, 1942 DeBoltJune 8, 1943 1 Jendrassik July 25, 1944 FOREIGN PATENTS Country DateFrance Mar. 10, 1926 Great Britain Mar. 4, 1932 'Italy Oct. 20, 1939

